A subnet representing the feasibility of minimal t-invariants. The feasibility of minimal t-invariants is represented to illustrate Equation (5). Place p
belongs to a p-invariant. It is adjacent to the pretransitions t1, t2,...t
and connected to the transition t
by a read arc. X and Y stand for the sets of t-invariants including the pre- and the posttransitions, respectively, which are contained in the corresponding dashed rectangles. Since p
does not carry tokens, t-invariants are not feasible if they contain transition t
without containing at least one of the transitions t1, t2,...t
. Thus, the read arc has to be bridged as described in Equation (5) to get feasible t-invariants.